The present invention generally relates to aircraft power systems and, more particularly, to auxiliary power generation for military aircraft.
Most mature military aircraft—such as the F-15—lack sufficient electrical power to run more modern power hungry systems, such as current electronic systems, for example, for avionics and weapons systems. One attractively simple, in concept, solution for increasing the available power is to modify the Airframe Mounted Accessory Drive (AMAD) to provide more power and install a larger generator on the AMAD. Usually this solution is difficult or impossible to achieve for at least two reasons: (1) no empty volume exists within the aircraft for a larger generator and AMAD to grow into, and (2) changing the AMAD and generator is cost prohibitive. Other options, however, are typically less attractive or not feasible for various reasons. For instance, a pop-up air scoop could be deployed to drive a Ram Air Turbine (RAT) that would drive a generator. This solution, for example, imposes additional aerodynamic drag on the aircraft, which could adversely affect aircraft performance—unacceptable for military fighter aircraft such as the F-15, and incurs a large amount of weight and mechanical complexity compared to the amount of extra power generated so that it is inefficient from both a cost and energy standpoint.
FIGS. 1A, 1B, and FIG. 3 illustrate a typical AMAD and accessory configuration 100 for an existing military aircraft—such as the twin engine F-15. The following discussion, however, may also be applicable to other multiple engine aircraft and to single engine aircraft. An example of a mature, single engine, military aircraft is the F-16. Configuration 100 may include at least one AMAD 102, to which may be mounted various power accessories, such as a power conversion hydraulic pump 104, an electric generator 106, and a utility hydraulic pump 108. AMADs 102 may be mounted to a bulkhead 110, the general location of which is indicated by a dashed line in the diagram of FIG. 1B. A jet fuel starter 112 may be provided for supplying power to start the main jet engines (not shown) of the aircraft. When starting the main engines of the aircraft, jet fuel starter 112 may provide power through a central gearbox 114 via drives 116 to AMADs 102. AMADs 102, in turn, provide power for starting to the main jet engines through power take off (PTO) shafts 118. PTO shafts 118 may be connected to AMADs 102 at an AMAD end 120 and, at an engine end 122, to a main jet engine or an engine mounted gearbox 124, also shown in FIG. 2. After the main engines have been started, central gearbox 114 may operate to disconnect jet fuel starter 112 from power communication with AMADs 102 so that each AMAD 102 may be driven by a main engine, for example, through an engine mounted gearbox 124 via a PTO shaft 118, and, in turn, AMAD 102 may drive the power accessories, such as power conversion hydraulic pump 104, electric generator 106, and utility hydraulic pump 108. Electric generator 106 may be driven through a gearbox 107 connected between AMAD 102 and electric generator 106.
FIG. 2 shows a view for a typical, mature military aircraft 125 of empty volume or unused space 126 around the drive shaft connecting the engine to the AMAD. Unused space 126 is located between the engine and the AMAD on the opposite side of bulkhead 110 from that on which AMAD 102 is mounted, so that FIG. 2 shows engine mounted gearbox 124, and PTO shaft cover 118′, underneath which PTO shaft 118 is located, extending between engine mounted gearbox 124 and bulkhead 110. Thus, unused space 126 is generally considered to be unusable for the purpose of providing larger power accessories for AMAD 102. Furthermore, as described above, typical mature aircraft don't have excess space around their existing generators—such as generator 106—on the opposite side of bulkhead 110 from that shown in FIG. 2 in which to replace the existing generator with a larger one.
As can be seen, there is a need for significantly increasing the electrical power generation capacity of existing mature military aircraft while avoiding costly and perhaps impossible modifications to the existing AMAD and generator configuration of such aircraft. There is also a need for significantly increasing the electrical power generation capacity of existing mature military aircraft that uses available unused space and does not require changing the existing AMAD and generator. Furthermore, there is a need for providing for mature aircraft an attractive, cost effective electrical power solution where none existed and, therefore, enabling incorporation of present day and future electronic systems on mature aircraft, which may extend the life of aircraft like the F-15.